<p>Use the <code>instances</code> attribute to specify the number of app instances that you want to start upon push:</p>

<pre>
---
  ...
  instances: 2
</pre>

<p>We recommend that you run at least two instances of any apps for which fault tolerance matters.</p>

<p>The command line option that overrides this attribute is <code>-i</code>.</p>
